1. Field of the Invention
The present invention relates to a method and apparatus for accurately detecting the position, density, and the like of each particle distributed in a three-dimensional sample.
2. Description of the Prior Art
Many conventional image processing techniques process two-dimensional images due to structures of image processing equipments. This is because conventional image processing equipments can process two-dimensional information but cannot directly process three-dimensional information.
FIG. 10 shows a conventional particle analysis method. Two-dimensional gray image data of three-dimensionally distributed particles 1 is obtained. In an image processing equipment, gray image data has unit data representing a unit image (pixel) 3 called a pixel. Each data has tone information. Referring to FIG. 10, reference numeral 5 denotes a pixel image representing an image of one particle using unit data. It is determined whether each pixel data serves as a peak density point with respect to neighboring data. If so, this pixel data is set to "1"; otherwise, it is set to "0", thereby obtaining a particle image using 1 or 0, i.e., binary image data. Reference numeral 7 denotes a pixel image of one particle using this binary image data. When this pixel image is shrinked, the position of each particle is obtained (Japanese Patent Application No. Hei 4-71593). Reference numeral 9 denotes a shrinked pixel image of one particle.
On the other hand, a method of obtaining a stereoscopic image from a two-dimensional tomographic image group is known as three-dimensional image processing (Japanese Patent Application No. Sho 60-155109). A method of reconstructing a two-dimensional image group obtained by viewing a two-dimensional image group from different directions is a well-known method in X-ray CT or the like.
As a method of obtaining a two-dimensional tomographic image, a light scattering method for causing a laser beam to be incident in a crystal to observe scattered light is known (Japanese Patent Application No. Sho 54-109488). In addition, a "Method and Apparatus for Measuring Particle Distribution" for analyzing an image of this scattered light and obtaining the density distribution of particles contained in a sample is known (Japanese Patent Application No. Sho 63-49848).
A dust counter (laser scattering method) for causing a laser beam to be incident on a dust or the like and counting down pulses of light scattered by the dust or the like is conventionally known for detection of dust and air bubbles in a liquid or air. A method of obtaining a grain size distribution using angular dispersion of light scattering caused by particles is also known.
As shown in FIG. 11, however, when slices 11 are scanned with a laser beam to sequentially observe tomographic images of a crystal or fluid in which particles are contained, the same particle 1 is observed in different sizes on different slices 11. A particle image on each slice is obtained as gray image data. In such a tomographic image group, if a plurality of particles are present, the plurality of particles overlap each other to fail to recognize the number of particles and their sizes in a conventional two-dimensional image processing method.
In the dust counter described above, a laser beam portion for radiating a given particle may not be a peak intensity portion but a tail intensity portion, so that the given particle is detected by this tail portion. In this case, the size of the particle is measured to be smaller than the actual size. To avoid this, scattering images must be obtained with shifts of the laser beam. However, of all the scattering images obtained by shifting the laser beam, a scattering image having a highest level of scattering from the given particle cannot be automatically selected.